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Magnetron - the microwave producing tube includes a heated filament cathode, multiple resonant cavities with a pair of permanent ceramic ring magnets to force the electron beams into helical orbits, and output antenna...The filament and cathode are one in the same and made of solid tungsten wire, about .020" (.5 mm) diameter, formed in a helix with about 8 to 12 turns, 5/32" (4 mm) diameter and just over 3/8" (9.5 mm) in length.The cathode is coated with a material which is good for electron emission... Low output. Occurs as cathode emission decreases from long use. Symptoms: Reduced cooking power.
RD's answer is correct, but there is more. There is also heating of the transformer. With all that, all microwave ovens exhibit a decease in output power with time, but it is not a constant decrease. If you start a cold oven (hasn't been used for at least 6 to 8 hours,the output power decreases by about 10% within 10 to 15 minutes and then is stable for hours. We've tested many (at least 50) ovens and they all exhibit this behavior. But all this is done under controlled laboratory conditions. In the home, there are other factors having to do with the food being heated that makes it seem as if the heating is not consistent - such things as food mass, starting temperature, shape, and lots more influence this.
Wood-burning stoves (eg for heating your living room) are similarly misleadingly rated. Manufacturers eager to flog you one quote "max outputs" (in BTU or kW), but this is with the stove flogged to melting point, dampers fully open and burning a few shovelfuls of whatever that stuff was the mad professor in Back to the Future 3 jammed into the firebox of the steam train...Consequently most home stoves don't come close to the manufacturers' quoted outputs.Instead, because people were being mislead in this way, companies are now having to switch to "nominal" outputs, which is supposed to be more representative (like an average) of heat output.Maybe microwaves should do the same...?(Meanwhile, this thread is so interesting I might recommend it to Diana as a Question of the Week...)Chris
I think Neil and Chris mislead you slightly there Geezer. It is well known that all Americans are millionaires (The streets are paved with gold. It's true, I saw it) so I'm guessing that you, Mr Geezer, you are the 'pocket money.. Don't act too surprised when they call you to take care of the tickets, just remember to smile..Hey, can I come too?
Quote from: yor_on on 09/02/2010 01:16:17I think Neil and Chris mislead you slightly there Geezer. It is well known that all Americans are millionaires (The streets are paved with gold. It's true, I saw it) so I'm guessing that you, Mr Geezer, you are the 'pocket money.. Don't act too surprised when they call you to take care of the tickets, just remember to smile..Hey, can I come too?Of course ewe can come chum..more the merrier..erhmm..I just received a brochure about the ship !![attachment=11289]errhm !!